Indoor salt water pool, getting it balanced - crazy high salt levels

[steveg_nh]

Hey All,

I'm helping another friend in town (yes, this seems to be a theme ) get their newly refurbished indoor pool balanced. This is a plaster pool, that is coated with epoxy, so I'm assuming it's epoxy paint, and should be managed/cared for as a plaster pool.

Anyway, I went over because he is concerned it was starting to turn green. My initial reaction when I saw it was that it did not look like algae, but rather just the depth and color of the water given the lighting and such. Another friend of ours (the one I helped with their lagoon style pool last year) suggested that it looked like the "color" of bleach, and maybe was way too high in chlorine. We weren't' sure, but the water was crystal clear, you could spot a dime in the deep end, but just a slight greenish/blue tint.

Anyway, I took a full set of test results, and was shocked to find the salt level and pH off the charts. And some things nonexistent from what I can tell.

The pool is likely around 22-25,000 gallons, which I'll confirm tonight after adding some bleach, and retesting to see the impact of the added chlorine (to calculate gallons). It has a Pentair itellichlor SWG. Separate spa that can mix with pool water. Propane/electric heater as well. Cleaning the SWG cell is going to be a real pain given how the pool builder installed it. It is directly behind and at the back of the heater. You cannot reach it easily at all, so that will be a PITA to check the plates for buildup. This pool will run all year long, so it will be more than a once/twice a season thing as is more common here in New England.

Anyway, this pool was completed (the remodel) and has had water in it for 2 weeks already. The builder didn't really do all that much to help the owner understand how to manage the water, so it's time for us to take over.

Here's the results:

Cl: 5
CC: 0.5
CYA: 0
TA: 0 (I assume, as the test went RED immediately upon adding the second reagent, never needed to add a single drop of the third reagent to get it to turn red)
pH: <6.6 (I think it's possibly lower and just off the scale low as we added sodium carbonate that we had, 4 pounds, and that showed zero change - working on this one right sway)
CH: 60
Salt: 8000ppm (average of 3 tests)

The plan of attack is this:

1. Get PH right, asap. The owner adding, as I instructed him to, Washing Soda last night. I will retest tonight.
2. Determine actual pool volume (tonight, with a bleach test)
3. Bring up TA to proper levels.
4. Bring up CH a bit (especially given it's a plaster pool behind the epoxy)
5. Run an OCLT to determine if there really is any algae in the water.
6. Dump about 25% of that salty water and refill with clean water.

Since it's an indoor pool, very little splash out will occur so the salt will take forever to disappear on it's own from use.

First question is how high salt levels like this might skew other tests. From what I can tell, they will not, but certainly that much salt is corrosive and not needed. The SWG is even flashing "HIGH SALT".

And second, please advise on CYA needs on an indoor pool where the impact of sun isn't there, and buffering of chlorine likely not critical.

Thanks all!

 

[Rollercoastr]

And second, please advise on CYA needs on an indoor pool where the impact of sun isn't there, and buffering of chlorine likely not critical.

20-30

Do you have a theory on how it got so acidic? My replastered pool has been thirsty for acid. Maybe the epoxy?

 

[steveg_nh]

No idea on why the ph is so low. I figured the same, that it would need acid due to the new remodel. But I don't believe the pool was replastered, but patched, and then painted with the epoxy. I'd have to ask Derek (the owner) how much of the actual plaster they repaired. But it was so low. I can only imagine the fill water was that low. Could the high salt levels have had an impact on that?

 

[pooldv]

Salt has no impact on pH, TA or the tests. Generally fill water has higher pH to prevent corrosion of plumbing, 7.6 or higher. TA at 0 means pH is in the 4s. The most common thing that crashes pH/TA is trichlor pucks, they are fairly acidic and steadily lower ph and TA until it crashes. Raise pH with Borax until it shows up on the test. Do this incrementally, add some, circulate for 15 minutes, test, repeat until it shows above 7.0 on the pH test. Then test TA and raise it with baking soda to 60-80.

Edit: Raise TA to 50 with baking soda first and then work on pH.

 

[steveg_nh]

Thanks. I had a feeling PH was off the charts low. This is new fill water with a SWG, so no pucks. I will get ph in check, and then retest all.

We'll bring CYA up to 20 too.

 

[domct203]

If the water is clear, but has a yellow-greenish color to it there could be metals in the water.

Iron is usually the most common culprit, but if the TA is truly zero, your pH is most likely closer to 4 and this highly acidic water could have etched away the copper heat exchanger in the pool heater, putting copper into the water, especially if it has been that way for weeks. How was the pool re-filled (well/city/truck)?

Is there any brown or black staining in the pool?

 

[pooldv]

I'm going to backtrack on raising pH first. Raise TA first to 50 with baking soda and then work on pH.

It is easier to raise CYA to 30 and maintain tain it because it shows up better on the test when it is 30 than it does at 20.

 

[steveg_nh]

Don, it will was filled by pool water trucks, but that water is usually pulled from local city water. No visible staining either.

Pooldv, sounds good. Given that it is 0, is it as easy as going from 0 to 50 or so with pool math, or could it also be so low it needs way more baking soda? Assuming 0 to 50 as per poolmath, we need 16 pounds of it just to get to 50 for TA.

 

[Isaac-1]

On the topic of CYA what I generally do with my indoor pool is boost CYA up to 30 ppm then wait for it to drift down to 20 ppm and then re-boost it (typically once per year or so as CYA does slowly oxidize)

 

[domct203]

Don, it will was filled by pool water trucks, but that water is usually pulled from local city water. No visible staining either.

Pooldv, sounds good. Given that it is 0, is it as easy as going from 0 to 50 or so with pool math, or could it also be so low it needs way more baking soda? Assuming 0 to 50 as per poolmath, we need 16 pounds of it just to get to 50 for TA.

I get 293oz by weight, or 18.3 lbs of baking soda to go from zero to 50ppm TA in 25K gallons.

I would assume zero and add it all. If you happened to overshoot by 20% you would be at 60ppm or so, no big deal. I would think that you would see 20ppm in the TA test, so you are most likely at 10ppm or less.

 

[pooldv]

Agreed.

 

[steveg_nh]

That's my thinking. I'll
Post later. Heading over there in a bit.

 

[steveg_nh]

Ok, so I'm back with an update.

We have pH and TA under control now. Now going to work on CH and a bit of stabilizer. New readings are:

FC: 20!
CC: 0.5
pH: 7.6
CH: 50
TA: 60
CYA: 0
Salt: 7800

A gallon of bleach was added yesterday by the owner. Obviously the pool isn't close to 25,000 that the pool remodeler told him. I'm not surprised either, as I was thinking 18,000, but I'm thinking it's more like 12-15k. In fact, maybe even less? To try to calculate size, I added one more quart of bleach and FC went to 24. Up 4. Using poolmath to figure out the impact on a certain size pool, I'm coming out to like 9,000 gallons. Can that be right? I added washing soda as if it was a 15,000 pool and it responded correctly.

With FC that high, we are letting FC float down (SWG is off) and I will do the math/test again when FC is more reasonable like 4 or 5. Given it's an indoor pool, should we add some stuff to consume some FC?

The owner still needs to figure out how much water to swap if he wants to drop the salt level. The SWG is not happy, and is flashing high salt. Recommended level on SWG is 3400.

This is the best part. He was given a water test result sheet from the pool store by the builder. They measured salt at 5400 and FC at 0! Granted their test water was before the FC spike, but I got 5 just after they pulled the water for the test. Maybe it sat too long?

Anyway, still not convinced there's an algae issue. Here's some pics. Any guess on pool size? I know, hard to do from a pic. You can see the slight tint to the water though...We did think there was improvement from day 1, with the PH change, but not sure how that would even do it.

 

[pabeader]

Make sure that you adjust Pool Math to account for the strength of the bleach you used. That might account for the difference.

 

[domct203]

Wow, that's an awesome pool area.

 

[steveg_nh]

We did. 8.25%. It's a 7' deep end, 3' shallow end. Could it really only be 9-10k gallons? I'll have to test again like I said, when the level drops.

 

[ping]

I would drain about 50% of the water to lower the salt level and it will also lower the FC level. After it is filled, balance the water and I would run the CYA at 20ppm.

Hard to tell by the pictures but I say it could very easily be only 10,000 gallons.

 

[steveg_nh]

I was thinking the same, about 50% of the water. He's talking to the remodeler today to see what he wants to do, since he added all this salt.

 

[YippeeSkippy]

Try to estimate the gallons by breaking the pool up in to two sections in your mind as its unusual shape suggests such. Using pool math measure each one separately and then take into consideration all the step/seat areas.

Sidenote: does this pool have space to actually swim laps in? Its so curvy its hard to tell from the pictures.

 

[steveg_nh]

We did that and came up with about 15,000. Just the results of adding the 32oz of bleach said much smaller. As for laps, not really. About a 16' diameter circle and then a triangle shaped section. Connected by a 7' side section...